Method for measuring distance and position using spectrum signal, and an equipment using the method

ABSTRACT

Under a multi-path environment, the receive timing for an incoming wave of the minimum propagation delay time cannot be accurately measured in the prior art. By using the delay profile created by delay profile creating section  102  and the first threshold value  330  received from the first threshold value calculation section  105 , the first threshold value timing detection section  103  selects only the earliest receive timing exceeding the first threshold value, from all the timings that the correlation value in the delay profile becomes a maximum. By using the receive timing and the second threshold value  331  received from the second threshold value calculation section  107 , the reference timing calculation section  106  selects the reference timing required for calculating the receive timing for the incoming wave of the minimum propagation delay time. The timing delayed by a previously set timing behind said reference timing is sent from the receive timing calculation section  108  as the receive timing  113  of the incoming wave of the minimum propagation delay time.

BACKGROUND OF THE INVENTION

The present invention relates to terminal equipment for measuring itsown position, particularly to equipment for measuring distances andpositions using the radio waves emitted from base stations fixed on theground, including CDMA base stations.

The principles of distance measurement using a spread spectrum signalare described using FIG. 9. The station for transmitting the spreadspectrum signal transmits this signal in send timing 400. Theaforementioned receiving station receives the spread spectrum signal andobtains receive timing 401. Differential time 402 between receive timing401 and send timing 400 is detected as the propagation time of thespread spectrum signal. The distance between the transmitting stationand the receiving station can be calculated by multiplying differentialtime 402 by the velocity of light. Because of the principles describedabove, distance measurement using a spread spectrum signal requires themeasurement of receive timing 401 at the receiving station.

Next, the principles of position measurement using a spread spectrumsignal are described. The distances to individual transmitting stationsare measured by the receiving station, subject to the principlesdescribed above. The use of the thus-obtained distances between thereceiving station and each base station and of the positions of the basestations enables the position of the receiving station to be detected bysolving the equation where the position thereof is taken as an unknownquantity. Details of one such detection method are disclosed in, forexample, Japanese Laid-Open Patent Publication No. Hei 7-181242 (1995).

To use spread spectrum signals for conducting distance or positionmeasurements in this way, it is necessary to measure the receive timingof the aforementioned spread spectrum signal at the terminal equipment.In Japanese Laid-Open Patent Publication No. Hei 7-181242 (1995), thefollowing method for measuring such receive timing is disclosed: thecorrelation values between the received signal and the predeterminedcode series for creating spread spectrum signals (hereinafter,collectively called the PN code) are calculated for each receivingevent, and a profile is created that shows the values corresponding tothe correlation values in each receiving event (hereinafter, thisprofile is called the delay profile); wherein an epitomized diagram ofthe delay profile is shown as 1 in FIG. 10, and the timing where thecorrelation value becomes a maximum in the delay profile is searched forand the corresponding timing is detected as the timing in which thespread spectrum signal is received. In the example of FIG. 10,“t_(prev)” is the receive timing.

SUMMARY OF THE INVENTION

During distance measurement and position measurement, it is important tomeasure the receive timing of the signal wave that has first arrived atthe terminal equipment, namely, the incoming wave of the minimumpropagation delay time. Consider the case that as shown in FIG. 11, aplurality of spread spectrum signals from a single spread spectrumsignal transmitting station are passed along different propagationroutes and received at terminal equipment as incoming waves 1 and 2different in both propagation delay time and signal intensity. In thiscase, the delay profile received takes the shape of delay profile 12, acombination of delay profiles 10 and 11 corresponding to incoming waves1 and 2, respectively. In this case, only receive timing 22 of incomingwave 2 can be detected with the prior art. In the example of FIG. 11,since incoming wave 1 has the minimum propagation delay time and isreceived in timing 21, receive timing for the incoming wave of theminimum propagation delay time cannot be measured using the prior art.As a result, receive timing measurement errors occur and this makesaccurate distance or position measurement impossible.

For these reasons, the use of the present invention enables the distancebetween a signal transmitting station and a signal receiving station tobe measured by creating a delay profile from the signal wave receivedfrom the signal transmitting station, then taking the startup timing ofthe delay profile as reference timing, and detecting the timing delayedby a predetermined value behind the reference timing.

To measure position, it is necessary to calculate the foregoingreference timing for at least three signal transmitting stations, thencalculate the differences in send timing between the correspondingsignal transmitting stations, and detect the position of the signalreceiving station from the respective relative time differences.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a structural diagram of terminal equipment, the firstembodiment of the present invention;

FIG. 2 is a flowchart of the receive timing measurement algorithm usedin the present invention;

FIG. 3 is a structural diagram of the delay profile creating section;

FIG. 4 shows an example of a delay profile;

FIG. 5 shows the first structural example of the first threshold valuecalculation section;

FIG. 6 shows the second structural example of the first threshold valuecalculation section;

FIG. 7 shows the first structural example of the second threshold valuecalculation section;

FIG. 8 shows the second structural example of the second threshold valuecalculation section;

FIG. 9 is a diagram explaining the principles of distance measurement;

FIG. 10 is an epitomized diagram of a delay profile;

FIG. 11 is an epitomized diagram of the delay profiles created when twoincoming waves are present.

DETAILED DESCRIPTION OF THE INVENTION

The receive timing measurement algorithm used in the present inventionis described using the flowchart shown in FIG. 2, and an example of thedelay profile shown in FIG. 4.

In first step 500, the correlation value between the received wave andthe PN code is calculated and delay profile 202 is created.

In step 501, threshold value 206 required for making a distinctionbetween incoming waves and noise (hereinafter, this threshold value iscalled the first threshold value) is calculated in delay profile 202. Atthis time, if in delay profile 202, the correlation value exceeds thefirst threshold value 206, this threshold value is used to judge that anincoming wave is present in the particular timing, and this thresholdvalue is sufficiently greater than the noise level.

In step 502, among all the timing that the correlation value becomesequal to the foregoing first threshold value 206, only the earliestreceive timing 205 is detected (hereinafter, the earliest receive timingis called the first threshold value timing).

In step 503, threshold value 207 required for detecting the timing inwhich the delay profile corresponding to the incoming wave is calculated(hereinafter, this threshold value is called the second thresholdvalue). At this time, the second threshold value 207 is used to detectthe timing in which the delay profile is started up from the noiselevel, and this threshold value is practically equal to the noise level.

In step 504, among all the timing that the correlation value becomesequal to the foregoing second threshold value 207, only the receivetiming 208 closest to and earlier than the first threshold value timing205 is detected as reference timing. Reference timing 208, therefore,denotes the timing in which the delay profile corresponding to theincoming wave is started up from the noise level.

In step 505, the timing 210 delayed by predetermined value 209 behindthe aforementioned reference timing 208 is calculated as referencetiming. This means that the incoming wave has arrived at the receivingstation in receive timing 210. Theoretically, predetermined value 209,under its noiseless state, has a tip value of 1.0. In actuality,however, since noise exists, an edge subsequent to the true leading edgeis detected as rise timing. This timing difference should therefore besubtracted to obtain a value from about 0.7 to 1.0.

During position measurement that uses spread spectrum signals, when thismeasuring method, as with one shown in Japanese Laid-Open PatentPublication No. Hei 7-181242 (1995), is to be used to conductmeasurements using the relative distance differences between eachtransmitting station and the receiving station, step 505 can be omittedand, instead, the reference timing 208 obtained in step 504 can be takenas receive timing 210.

The construction of the terminal equipment, one embodiment of thepresent invention, is shown in FIG. 1. The spread spectrum signal thathas been received by antenna 100 is sent to signal receiving section101, where the signal then undergoes high/medium-frequency receiving andbaseband signal demodulation. The spread spectrum signal, afterundergoing processing in signal receiving section 101, is further sendto delay profile creating section 102. The correlation value between thereceived spread spectrum signal and the PN code is calculated for eachreceiving event by delay profile creating section 102, which thencreates a delay profile that shows the values corresponding to thecorrelation values in each receiving event.

A structural example of delay profile creating section 102 using amatched filter is shown in FIG. 3. In FIG. 3, matched filter 200calculates the correlation value between the received spread spectrumsignal and the PN code created by PN code generator 201, and sends tosignal line 110 the value corresponding to the correlation value. Anexample of a delay profile created by delay profile creating section 102is shown as solid line 202 in FIG. 4. In FIG. 4, horizontal axis 212denotes receive timing and as the delay profile bring closer to the leftof the horizontal axis, the receive timing becomes earlier, that is, thepropagation delay time decreases. Vertical axis 213 in FIG. 4 denotescorrelation values.

The delay profile that has been created by delay profile creatingsection 102 is then held in delay profile holding section 115. Delayprofile holding section 115 can be, for example, a memory. The delayprofile, after being held in delay profile holding section 115, is sentto the first threshold value timing detection section 103, the firstthreshold value calculation section 105, reference timing calculationsection 106, and the second threshold value calculation section 107.

The first threshold value calculation section 105 calculates thethreshold value to be used for the first threshold value timingdetection section 103. A structural example of the first threshold valuecalculation section 105 is shown in FIG. 5. In this figure, the maximumvalue searching section 300 sends the maximum correlation value(existing in receive timing 203) of the delay profile received viasignal line 110. Multiplier 320 multiplies the maximum correlation value310 and coefficient C₀ and sends the results to the first thresholdvalue timing detection section 103 as the first threshold value 330.Coefficient C₀ is set to about 0.1. This avoids the likelymis-recognition of a side lobe caused by the characteristics of the bandlimiting filter within signal receiving section 101 during the creationof a delay profile; the side lobe being equivalent to a maximumcorrelation value 310 of about 0.1 in terms of magnitude.

Another structural example of the first threshold value calculationsection 105 is shown in FIG. 6. In this figure, noise power estimatingsection 301 estimates noise power using the delay profile received viasignal line 110, and generates an output of noise power 311. Thefollowing two methods are available to measure noise power:

(1) Approximating all received signal power to noise power

(2) Creating a profile repeatedly and calculating the dispersion in thepeak correlation values of the profiles

Method (2) above, although higher than method (2) in accuracy, requiresa long measuring time. Method (1) above, therefore, is used in FIG. 6.

Multiplier 320 multiplies the abovementioned noise power 311 andcoefficient C₁ and sends the results to the first threshold value timingdetection section 103 as the first threshold value 330. Coefficient C₁is set to a value from about 10 to 100 for this reason: when the noiseis considered to be white noise, momentary amplitude changes inaccordance with the required distribution, and in this case, if thenoise power is taken as the square of σ, the probability where themomentary amplitude exceeds 3σ is about {fraction (3/1000)}, which issufficiently slow as the probability of an measuring error occurring,and thus since an amplitude of 3σ is nine times the square of a in termsof power, C₁ needs only to be more than nine.

In FIG. 6, output 116 of signal receiving section 101 can likewise beused as the input of noise power estimating section 301. Also, the firstthreshold value calculation section 105 can have the structuralcomponents shown in both FIGS. 5 and 6, and send the greatest of thethreshold values calculated thereby, to the first threshold value timingdetection section 103 as the first threshold value 330. Or the firstthreshold value calculation section 105 can have the structuralcomponents shown in both FIGS. 5 and 6, and send the smallest of thethreshold values calculated thereby, to the first threshold value timingdetection section 103 as the first threshold value 330.

The first threshold value 330 received from the first threshold valuecalculation section 105 is used for the first threshold value timingdetection section 103 to generate the earliest receive timing in whichthe correlation value becomes equal to the first threshold value 330.The operation of the first threshold value timing detection section 102is described using FIG. 4. In FIG. 4, discontinuous line 206 representsthe first threshold value 330 received from the first threshold valuecalculation section 105. The earliest receive timing 205 that, in delayprofile 202, the correlation value becomes equal to threshold value 206is sent from the first threshold value timing detection section 103 tosignal line 111.

The second threshold value calculation section 107 calculates thethreshold value to be used for reference timing calculation section 106.A structural example of the second threshold value calculation section107 is shown in FIG. 7. In this figure, the same components as thoseshown in FIG. 5 as the first structural example of the first thresholdvalue calculation section 105, are each assigned the same number as thatof each shown in FIG. 5. Multiplier 320 multiplies the maximumcorrelation value 310 sent from the maximum value searching section 300,and coefficient C₂, and sends the results to reference timingcalculation section 106 as the second threshold value 331. CoefficientC₂ is set to about 0.1, which is based on data that was measured usingan experimental machine.

Another structural example of the second threshold value calculationsection 107 is shown in FIG. 8. In this figure, the same components asthose shown in FIG. 6 as the second structural example of the firstthreshold value calculation section 105, are each assigned the samenumber as that of each shown in FIG. 6. Multiplier 320 multiplies thenoise power 311 sent from noise power estimating section 301, andcoefficient C₃, and sends the results to reference timing calculationsection 106 as the second threshold value 331. Coefficient C₃ is set toabout 7, which is based on data that was measured using an experimentalmachine.

In FIG. 8, output 116 of signal receiving section 101 can likewise beused as the input of noise power estimating section 301. Also, thesecond threshold value calculation section 107 can have the structuralcomponents shown in both FIGS. 7 and 8, and send the greatest of thethreshold values calculated thereby, to reference timing calculationsection 106 as the second threshold value 331. Or the second thresholdvalue calculation section 107 can have the structural components shownin both FIGS. 7 and 8, and send the smallest of the threshold valuescalculated thereby, to reference timing calculation section 106 as thesecond threshold value 331.

The second threshold value 331 received from the second threshold valuecalculation section 107, the receive timing detection results receivedfrom the first threshold value timing detection section 103, and thedelay profile received from delay profile holding section 115 are usedfor reference timing calculation section 106 to calculate the referencetiming for obtaining the receive timing of the incoming wave of theminimum propagation delay time. The operation of reference timingcalculation section 106 is described using FIG. 4. In FIG. 4, single-dotdashed line 207 represents the second threshold value 331 received fromthe second threshold value calculation section 107. Reference timingcalculation section 106 compares the correlation value and thresholdvalue 207 in the receive timing 205 that has been received from thefirst threshold value timing detection section 103. If both valuesmismatch, the receive timing is advanced and the correlation value andthreshold value 207 in said receive timing are compared. This sequenceis repeated until the correlation value and threshold value 207 havematched, and the corresponding receive timing is sent as an output. Inthe example of FIG. 4, receive timing 208 in which the correlation valueand threshold value 207 match is sent as reference timing to signal line112.

The reference timing received from reference timing calculation section106 via signal line 112 is used for receive timing calculation section108 to calculate the receive timing for the signal wave that has firstarrived at the terminal equipment, namely, the incoming wave of theminimum propagation delay time. The operation of receive timingcalculation section 108 is described using FIG. 4. Timing 210 delayed bypreviously set timing 209 behind the reference timing 208 that has beensent from reference timing calculation section 106 is detected as thereceive timing for the wave of the minimum propagation delay time, andthe detected receive timing is then sent to signal line 113.

The above method when applied to delay profile 12 shown in FIG. 11 isdescribed. The first threshold value timing detection section can sendreceive timing 24 by using the appropriate first threshold value 330.Next, the reference timing calculation section can send receive timing20 by using the appropriate second threshold value 331. Furthermore,receive timing calculation section 108 can detect receive timing 21 byfirst measuring beforehand, under an environment having only oneincoming wave, timing difference 23 between all values from the startuptiming of the delay profile to the maximum value thereof, and then usingsaid timing difference 23 in receive timing calculation section 108.Receive timing 21 is the receive timing for incoming wave 1, the signalwave that has first arrived. In other words, even if two incoming wavesare received in overlapping form, it is possible to detect the receivetiming for the signal wave that has first arrived.

Based on the receive timing 113 sent from receive timing calculationsection 108, calculations for distance measurement or positionmeasurement are performed by distance/position measuring section 114.Distance/position measuring section 114 can use, for example, the methoddisclosed in Japanese Laid-Open Patent Publication No. Hei 7-181242(1995).

During position measurement that uses spread spectrum signals, when thismeasuring method, as with one shown in Japanese Laid-Open PatentPublication No. Hei 7-181242 (1995), is to be used to conductmeasurements using the relative distance differences between eachtransmitting station and the receiving station, processing by receivetiming calculation section 108 can be omitted and, instead, output 112of reference timing calculation section 106 can be connected to signalline 113 and the corresponding output value can be sent todistance/position measuring section 114. In this case, delay profilesare created using the signal waves received from at least three signaltransmitting stations, and then the first and second threshold valuesare created for each such delay profile. Subsequently, the startuptiming of each delay profile is detected and the differences in sendtiming between the corresponding signal transmitting stations are usedfor the receiving station to measure its position from the relative timedifferences between the signal transmitting stations.

The present invention enables accurate detection of the receive timingfor the first incoming wave arriving under the multi-path environmentthat a plurality of incoming waves are received in overlapping form.Thus, it is possible to minimize measurement errors at the terminalequipment that uses spread spectrum signals to conduct distance andposition measurements.

What is claimed is:
 1. A method for measuring distance comprising: afirst step to create a delay profile from a signal wave received from asignal transmitting station; a second step to detect a startup timing ofthe delay profile as reference timing, wherein the startup timingcorresponds to a timing when a correlation value of the delay profile isequal to a predetermined threshold value; and a third step to detect atiming delay by a predetermined value behind the reference timing as areceive timing for the signal wave; wherein the distance between thesignal transmitting station and signal receiving station is measuredfrom a difference between a transmitting timing of said signaltransmitting station and the receive timing.
 2. A distance measuringmethod set forth in claim 1, said second step further comprising: afourth step to calculate a first threshold value for distinguishing theincoming signal wave from noise in the delay profile; a fifth step todetect the earliest receive timing as the first threshold value timingin the delay profile, among all timings in which the correlation valuebecomes equal to the first threshold value; a sixth step to calculate asecond threshold value for identifying the startup timing of said delayprofile, the second threshold value being said predetermined thresholdvalue; and a seventh step to detect the earliest and closest receivetiming relative to the first threshold value timing as the referencetiming in the delay profile, among all the timings in which thecorrelation value becomes equal to the second threshold value.
 3. Aposition measuring method comprising: a first step for creatingindependent delay profiles from signal waves received from at leastthree signal transmitting stations; and a second step for detecting astartup timing of each of said delay profiles as a reference timing,wherein the startup timing corresponds to a timing when a correlationvalue of the delay profile is equal to a predetermined threshold value;wherein a time difference between the reference timing of each delayprofile and receive timing of signal transmitting stations correspondingto said delay profile are calculated, and positions of said signalreceiving stations are measured from each calculated time difference. 4.A position measuring method set forth in claim 3, said second stepfurther comprising: a third step to calculate a first threshold valuefor distinguishing said incoming signal wave from noise in each delayprofile; a fourth step to detect the earliest receiving timing as thefirst threshold value timing, in each delay profile, among all thetimings in which the correlation value becomes equal to the firstthreshold value; a fifth step to calculate a second threshold value foridentifying the startup timing of each said delay profile, the secondthreshold value being the same as said predetermined threshold value;and a sixth step to detect the earliest and closest receive timingrelative to the first threshold value timing as the reference timing inthe delay profile, among all the timings in which the correlation valuebecomes equal to the second threshold value.
 5. An equipment formeasuring distance using a signal wave transmitted from a signaltransmitting station comprising: means for creating a delay profile fromthe signal wave received from said signal transmitting station; meansfor calculating a startup timing of said delay profile as referencetiming, wherein the startup timing corresponds to a timing when acorrelation value of the delay profile is equal to a predeterminedthreshold value; means for calculating the timing delay by apredetermined value behind a reference timing as a receive timing forthe signal wave; and means for measuring the distance from a differencebetween a transmitting timing of said signal transmitting station andthe receive timing.
 6. An equipment set forth in claim 5, the referencetiming calculation means further comprising: means for calculating afirst threshold value for distinguishing the incoming signal wave fromnoise in the delay profile; means for detecting the earliest receivetiming as the first threshold value timing in the delay profile, amongall timings in which the correlation value becomes equal to the firstthreshold value; means for calculating a second threshold value foridentifying the startup timing of the delay profile, the secondthreshold value being the same as said predetermined threshold value;and a means for detecting the earliest and closest receive timingrelative to said first threshold value timing as said reference timingin the delay profile, among all the timings in which the correlationvalue becomes equal to the second threshold value.
 7. An equipment formeasuring positions using signal waves received from signal transmittingstations comprising: means for creating independent delay profiles fromthe signal waves received from at least three signal transmittingstations; means for calculating a startup timing of each delay profileas a reference timing, wherein the startup timing corresponds to atiming when a correlation value of the delay profile is equal to apredetermined threshold value; and means for calculating a timedifference between the reference timing of each delay profile andreceive timing of signal transmitting stations corresponding to saideach delay profile, and measuring positions of each of said signalreceiving stations from each calculated time difference.
 8. An equipmentset forth in claim 7, said reference timing calculation meanscomprising: means for calculating a first threshold value fordistinguishing the incoming signal wave from noise in each delayprofile; means for calculating the earliest receive timing as the firstthreshold value timing in each delay profile, among all timings in whichthe correlation value becomes equal to the first threshold value; meansfor calculating a second threshold value for identifying the startuptiming of each delay profile, the second threshold value being the sameas said predetermined threshold value; and means for detecting theearliest and closest receive timing relative to the first thresholdvalue timing as the reference timing in each delay profile, among allthe timings in which the correlation value becomes equal to the secondthreshold value.
 9. A terminal equipment for receiving spread spectrumsignals and measuring distances using these signals comprising: meansfor receiving a spread spectrum signal required for distancemeasurement, and creating a signal from the received signal; means forgenerating the same spread spectrum signal as that transmitted from aspread spectrum signal transmitting station, and creating a delayprofile for calculating a correlation value between the spread spectrumsignal and the received signal mentioned above; means for holding anoutput of the delay profile creating means; means for calculating afirst threshold value; means for detecting an earliest receive timing inwhich the correlation value becomes equal to the first threshold value;means for calculating a second threshold value; means for detecting asecond reference receive timing from the second threshold value, delayprofile, and a first reference receive timing; and means for calculatingthe receive timing of the signal from the second reference receivetiming.
 10. A terminal equipment set forth in claim 9, wherein saidreference timing calculation section selects the earliest and closestreceive timing relative to the first threshold value timing as thereference timing, among all the timing that the correlation valuebecomes equal to the second threshold value.
 11. A terminal equipmentset forth in claim 10, wherein said receive timing calculation sectiondetects the receive timing delayed by a predetermined value behind thereference timing as the receive timing for the signal wave.
 12. Aterminal equipment set forth in claim 9, wherein said calculationsection for the first threshold value detects, as the first thresholdvalue, the value obtained by multiplying the greatest of all thecorrelation values by a predetermined coefficient.
 13. A terminalequipment set forth in claim 9, wherein said calculation section for thefirst threshold value measures the noise power value of the receivedsignal and detects, as the first threshold value, the value obtained bymultiplying said noise power value by a predetermined coefficient.
 14. Aterminal equipment set forth in claim 9, wherein said calculationsection for the first threshold value measures, as the first availablevalue, the value obtained by multiplying the greatest of all thecorrelation values by a predetermined coefficient, and the noise powervalue of the received signal, then calculates, as the second availablevalue, the value obtained by multiplying said noise power value by apredetermined coefficient, and detects said first or second availablevalue, whichever is the greater, as the first threshold value.
 15. Aterminal equipment set forth in claim 9, wherein said calculationsection for the first threshold value measures, as the first availablevalue, the value obtained by multiplying the greatest of all saidcorrelation values by a predetermined coefficient, and the noise powervalue of the received signal mentioned above, then calculates, as thesecond available value, the value obtained by multiplying said noisepower value by a predetermined coefficient, and detects the first orsecond available value, whichever is the smaller, as the first thresholdvalue.
 16. A terminal equipment set forth in claim 9, wherein saidcalculation section for the second threshold value detects, as thesecond threshold value, the value obtained by multiplying the greatestof all said correlation values by a predetermined coefficient.
 17. Aterminal equipment set forth in claim 9, wherein said calculationsection for the second threshold value measures the noise power value ofthe received signal mentioned above and detects, as the second thresholdvalue, the value obtained by multiplying said noise power value by apredetermined coefficient.
 18. A terminal equipment set forth in claim9, wherein said calculation section for the second threshold valuemeasures, as the first available value, the value obtained bymultiplying the greatest of all said correlation values by apredetermined coefficient, and the noise power value of the receivedsignal mentioned above, then calculates, as the second available value,the value obtained by multiplying said noise power value by apredetermined coefficient, and detects said first or second availablevalue, whichever is the greater, as the second threshold value.
 19. Aterminal equipment set forth in claim 9, wherein said calculationsection for the second threshold value measures, as the first availablevalue, the value obtained by multiplying the greatest of all saidcorrelation values by a predetermined coefficient, and the noise powervalue of the received signal mentioned above, then calculates, as thesecond available value, the value obtained by multiplying said noisepower value by a predetermined coefficient, and detects said first orsecond available value, whichever is the smaller, as the secondthreshold value.
 20. A terminal equipment for receiving spread spectrumsignals and measuring positions using these signals comprising: meansfor receiving a spread spectrum signal required for positionmeasurement, and creating a signal from the received spread spectrumsignal; means for generating the same spread spectrum signal as thattransmitted from a spread spectrum signal transmitting station, andcreating a delay profile for calculating the correlation value betweensaid spread spectrum signal and the received spread spectrum signal;means for holding an output of the delay profile creating means; meansfor calculating a first threshold value; means for detecting an earliestreceive timing in which a correlation value becomes equal to the firstthreshold value; means for calculating a second threshold value; andmeans for calculating a second reference receive timing from said secondthreshold value, delay profile, and a first reference receive timing.21. A terminal equipment set forth in claim 20 comprises a means forcalculating the signal receive timing from said second reference receivetiming.